IGMP in latest 6th Gen AirPort Extreme Base Station (mini Tower model)

There is zero mention of it in the manual.

There is zero info released by apple in documents.. at least that I can find.

It is noted as existing in the 6.3 utility.. and is off by default.

(IGMP = internet group management protocol, allows routers to learn which multicasts you want to receive. IGMP snooping is done by switches so they only send multicasts to ports where hosts actually want them.)

I really doubt this is a biggie.. turn it on for Multicast when you use iTunes store or TV from netflix etc. See if it does anything .. !!

Multicast is becoming more commonly used to broadcast IPTV. BT in the UK for example delivers linear TV channels over multicast on their BT Infinity fibre broadband and some of these are even in HD. Multicast sends the same datastream to all ethernet/wifi ports on the particular multicast network. The advantage of this is that the server doesn't have to send multiple individual stream to multiple devices on the same network. It sends 1 stream and the network hardware floods all ports with the stream. The disadvantage is if a device on a network does not want to consume the multicast stream then its effective bandwidth is reduced because it gets the stream regardless of the fact it doesn't want it - particularly important with wifi. IGMP "listens" to each ethernet/wifi port and works out whether the individual port has initiated a multicast request. If it has not then the multicast stream is not sent to that port and it saves bandwidth. Turning this feature on for most people will either not be noticable if you don't use multicast or will help network speed for devices not using multicast.